An information processing apparatus for generating an image obtained by encoding desired information such as a QR Code® is used in a three-dimensional shape measurement apparatus or a position and orientation estimation apparatus in a decoding imaging capturing apparatus.
Three-dimensional shape measurement apparatuses for measuring the three-dimensional shape of a target object have been used in a variety of industrial fields such as parts inspection in factories and biometric shape measurements in the medical field. Particularly, a noncontact measurement method is effective when an apparatus may contact a target object to deform and damage it.
Various methods are proposed as the three-dimensional shape measurement method. A typical example is a space encoding method. According to the space encoding method, a projector projects an encoded pattern on a measurement target object on a measurement table, light reflected by the measurement target object is captured, and the pattern from the captured image is decoded, thereby obtaining the positions of a pair of points (corresponding points) corresponding to the identical points on the projected pattern image and the camera image. The positions of the corresponding points allow obtain a three-dimensional shape (projection and recess positions) to be obtained on the surface of the measurement target object in accordance with the principle of triangulation. An encoding method using a combination of a plurality of time-series pattern light beams and an encoding method using a combination of a plurality of spatial pattern light beams are available as information used for the above encoding.
An encoding method using a combination of a plurality of spatial pattern light beams is disclosed as an example of three-dimensional shape measurement in Thomas P. Koninckx, Andreas Griesser, Luc Van Gool: “Real-time Range Scanning of Deformable Surfaces by Adaptively Coded Structured Light”, Proc. IEEE Int'l Conf. 3-D Digital Imaging and Modeling, pp. 293-302, 2003. In this example, a projector projects, on an object, a pattern characterized by an intersection of two straight lines having different directions. A camera captures light reflected by the object, thereby measuring a three-dimensional shape. The practical procedures will be described below. First, multiple lines (base pattern) used for measurement and a line (code line) having a direction different from the base pattern so as to cross the base pattern are generated as a projection pattern image. The projector projects the projection pattern image on the object, and the camera captures the object projected with the projection pattern image. A camera coordinate system obtains an intersection between the base pattern and the code line, and an epipolar line passing through the intersection is obtained in projector coordinates. At this time, the epipolar line is obtained using a fundamental matrix obtained by calibrating the camera and the projector in advance. The intersection between the epipolar line and the code line is obtained in projector coordinates. A base pattern line nearest to this intersection is specified, thereby making the camera and the projector associate with each other. Finally, the three-dimensional position of each point of the base pattern is obtained in accordance with the principle of triangulation.
However, in Thomas P. Koninckx, Andreas Griesser, Luc Van Gool: “Real-time Range Scanning of Deformable Surfaces by Adaptively Coded Structured Light”, Proc. IEEE Int'l Conf. 3-D Digital Imaging and Modeling, pp. 293-302, 2003, the position of the intersection between the epipolar line and the code line becomes ambiguous due to the shape of an object. The nearest base pattern line may not be specified. From this reason, when the median value of the width of lines of the base pattern formed in the captured image is equal to or less than a predetermined value, the line width of the base pattern is increased in the next capturing operation to readily specify an intersection, thereby solving the ambiguity in association.
For this reason, in Thomas P. Koninckx, Andreas Griesser, Luc Van Gool: “Real-time Range Scanning of Deformable Surfaces by Adaptively Coded Structured Light”, Proc. IEEE Int'l Conf. 3-D Digital Imaging and Modeling, pp. 293-302, 2003, the number of lines to be displayed is reduced due to an increase in line width of the base pattern, thereby undesirably reducing the measurement density in three-dimensional measurement.